Recently, with rapid technical development in industries of mobile phones, notebooks, and electric automobiles, a worldwide demand for a portable energy source has been increasingly enlarged. Particularly, utilization of a lithium secondary battery as a portable energy source has been explosively increased. At present, lithium battery industry is actively developed in South Korea, Japan, and China, and with the increased demand for lithium batteries, the consumption of lithium for use in the lithium batteries practically increases. Further, lithium is also used as a material for producing tritium in thermonuclear fusion that is expected to be a next-generation energy source, the demand for lithium further increases.
It is estimated that the seawater contains about 230 billion tons of lithium ions, so that peoples now perceive it as an important lithium source. However, since the concentration of lithium in the seawater is very low as 0.17 mg/liter, when considering the economical feasibility for recovering lithium ions, a need exists to provide a system for selectively recovering lithium ions with low cost.
In order to recover lithium from a lithium-dissolved solution, particularly seawater, an ion exchange adsorption method, a solvent extraction method, a coprecipitation method, and the like haven been researched, and among the above methods, the ion exchange method is evaluated to be one of the most preferable lithium recovery methods because it uses manganese oxide-based inorganic adsorbent that provides an ion exchange characteristic of very high adsorption selectivity with respect to lithium, thereby efficiently recovering lithium ions. Accordingly, a variety of manganese oxide-based inorganic adsorbents are being developed (see Ind. Eng. Chem. Res., 40, 2054, 2001). The adsorption of lithium ions is carried out in such a way that upon topotactic extraction of lithium ions through acid treatment, lithium-manganese oxides having a spinel structure and acting as a precursor exhibit excellent adsorption selectivity with respect to lithium ions in an aqueous solution and thus have high functionality as a high-performance absorbent, so that the lithium ions in the solution are adsorbed with ion exchange between hydrogen ions and lithium ions, and then the lithium ions adsorbed on the inorganic adsorbent are recovered by further ion exchange between hydrogen ions and lithium ions. Thus, such a manganese oxide-based inorganic adsorbent has an advantage such as a repetitively reusable feature.
In case of applying a manganese oxide in the form of powders to a solution, particularly seawater, the manganese oxide powders should not be lost. To this end, according to Ind. Eng. Chem. Res., 41, 4281, 2002, a system is proposed in which a manganese oxide is also introduced when a separator membrane is manufactured using polyvinylchloride (PVC). However, this system has drawbacks in that a solution, particularly seawater should be supplied from exterior through additional addition of pressure, the amount of manganese oxide adsorbent introduced that is directly related to the recovery amount of lithium is limited, and a portion coated with PVC has a degraded adsorption performance.
Further, in the conventional process of processing a great quantity, e.g. more than tens of kg, or more than a ton of lithium-manganese oxide powders in the form of a particulate with the size of about 10 μm with an acidic solution to form manganese oxides, a bulky water bath and a stirring device efficiently promoting a reaction between the acidic solution and the powders are required, and separation and drying processes with respect to liquid obtained from the treatment with the acidic solution are further required. Like this, the conventional lithium ion recovery device and the lithium ion recovery method using the same are very complicated and troublesome device and method, and have to add careful attention to recovering processes.